Michelin
iPF Noob
Just click on them and hit upgrade.
Just FYI - it's usually better value to sell a smaller farm/habitat first and then buy the bigger one (as long as you aren't at maximum habitats with no room to move dragons to other habitats in the meantime).
You usually pay the same price to upgrade that it costs to buy a new one and at least you get back half what you paid for the smaller one if you sell it first!